1. Field of the Inventions
The invention relates generally to semiconductor packaging and specifically to improving heat dissipation within a semiconductor chip.
2. Background Information
Heat dissipation is essential in semiconductor chips. In the extreme, if a semiconductor chip is allowed to get too hot it can damage the chip. Even outside of this extreme semiconductor chips are designed to operate within a particular temperature range. In order to maintain a chip within its operating temperature range, heat must be drawn away from the chip. As chips become higher performance, they pose a greater challenge as they consume more power and generate more heat.
FIG. 1A illustrates a basic semiconductor chip package in cross-section. FIG. 1B is a close up view of semiconductor chip package 100. It should be noted that all figures in this disclosure are conceptual representations and components contained in these diagrams are not necessarily to scale. The figures are presented to illustrate the aspects and embodiments related to the present invention and should not be taken to be limiting.
Beyond semiconductor functional die 102, the semiconductor chip comprises some sort of electrical or optical interface. In FIGS. 1A and 1B this is depicted by ball grid array (BGA) 104. Functional die 102 is semiconductor substrate which has undergone a series of etching and deposition steps to fabricate circuitry upon the semiconductor substrate. The fabricated substrate is then diced into individual dies. Wire bonds 106 are used to connect various bond pads on functional die 102 to BGA 104. Finally, wire bonds 106 and functional die 102 are encased by package material 108, which can be an epoxy mold compound. Examples of the package material include epoxies or resins and are often injection molded.
In order to dissipate heat in chip 100, heat is conducted away from functional die 102 to the outside environment through package material 108. In high power applications, package material 108 can be attached to an external heat sink and in the extreme the heat since could even be coupled to an electric fan. However, to reach the heat sink, the heat is first drawn through the package material. To this end previous solutions have used more expensive mold compounds for the package material having a higher thermal conductivity (e.g. 3 W/mK instead of the standard 1 W/mk). However, in addition to the expense, these mold compounds are less reliable, and are more difficult to use in the transfer molding operation.
FIG. 2A illustrates a semiconductor chip where an internal heat spreader is used to aid in the dissipation of heat. Heat spreader 202 typically comprises a metal such as copper for conducting heat away from functional die 102. However, heat still needs to be conducted by package material 108 between functional die 102 to heat spreader 202. Heat spreader 202 can then conduct the heat off the chip and is typically exposed to the air (or external environment).
FIG. 2B illustrates the use of a dummy die to improve thermal dissipation. To reduce the distance that heat is conducted, dummy die 204 is placed on top of functional die 102 putting it in closer thermal proximity to the heat spreader 202. Dummy die 204 is typically a die segmented from an unfabricated silicon substrate.
Other chip configurations such as cavity-down or flip chip packages have also be been employed. However, these configurations are much more expensive in fact they are two to five times more expensive to manufacture. Accordingly, various needs exist in the industry to address the aforementioned deficiencies and inadequacies.